IHG 05 Base Excess and Critical Care in the past and in the future Ivar Hejde Gøthgen M.D., D.M.Sc.

IHG 05

Base Excess and Critical Care in the past and in the future

Ivar Hejde Gøthgen M.D., D.M.Sc.

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Content

• Acid-base basic

• Scientist in the acid-base story

• Instruments in the acid-base story

• The future and Base excess

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Acid Base (concept of neutrality) _______________________________________________________________________

pN = [H+] = [OH-] (=neutrality)

pH = 6.80 [H+] = [OH-] = 160 nmol/l= neutrality at 37 oC

pH = 7.40[H+] = 40 nmol/l [OH-] = 640 nmol/l= Alkaline offset of 0.6 pH unit

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pH = 6.8Extracellularfluid pH = 7.40

Blood and extracellular fluid serve as sink for metabolic produced acids

H+

Acid Base (the simple model) _______________________________________________________________________

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Acid Base (the acid production) _______________________________________________________________________

Fixed Acids production [H+] : 60 mmol/24 hour => 700 nmol/sec

Volatile Acids production [H+] :13 mol/24 hour => 150000 nmol/sec> 200 times the fixed acids

Total extracellular free [H+] : 40 nmol/l * 15 l => 600 nmol

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Buffer Base 50 mmol/lBuffer base = H+ acceptors

_____________________________Red cell Hemoglobin 35%Red cell Bicarbonate 18%Plasma Bicarbonate 35%Plasma Proteins 7%Others (Phosphate ect.) 5%

Acid Base (the Metabolic component I ) _______________________________________________________________________

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BASE EXCESS and the Acid-Base nomogram

Base excess was introduced by Ole Siggaard Andersen for almost 50 years ago.

While pH and pCO2 are directly measured, the metabolic component, defined as Base excess, is calculated from pH and pCO2 using the Henderson-Hasselbalch equation and the Van Slyke equation.

By using base excess the acid base status is made simple and clinical useful.

Acid Base (the Metabolic component II) _______________________________________________________________________

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Can you go to a Pharmacyand buy a bottle of Base excess ?

Acid Base (the Metabolic component III) _______________________________________________________________________

BASE EXCESS

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The Van Slyke equation(= The equation for the CO2 equilibration curve of blood in vitro)

a-24.4 = -(2.3*b+7.7)*(c-7.40)+d/(1-0.023*b)

where:a = bicarbonate concentration in plasma (mmol/l)b = hemoglobin concentration in blood (mmol/l)c = pH of plasma at 37 oCd = base excess concentration in blood (mmol/l)

Acid Base (the Metabolic component IV) _______________________________________________________________________

(Scand J Clin lab Invest 1977:37,Suppl 146:15-20)

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pH: as a measure of the activity of free hydrogen ions.

pCO2: as a measure of the respiratory component, the activity of free CO2 in the blood.

Base Excess: as a measure of the metabolic component, (the concentration of titratable hydrogen ion in the extracellular fluid).

Acid Base (the acid-base status) _______________________________________________________________________

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Acid Base (the acid-base status)

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Respiratory changes alongThe bufferlines


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Metabolic changes acrossThe bufferlines


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concentration of freeH YD RO G EN IO N in p lasm anano m ol/L

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pH in arteria l p lasm a

ACID EM IA N O R M AL ALKALEM IA

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concentration of titratab le H YDR O G EN IO N in extracellu lar flu id m m ol/L

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S iggaard-Andersen Acid-Base C hart

Bicarbonate

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Content

• Acid-base basic




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S.P.L. Sørensen 1868-1939

L.J. Henderson 1878-1942

K.A. Hasselbalch 1874-1962

Donald D van Slyke 1883-1971

Poul Astrup 1915-2000

John W. Severinghaus 1922-

Ole Siggaard-Andersen 1932-

Scientist in the acid-base story

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Søren P. L. Sørensen 1868-1939

Protein Chemist at the Carlsberg brewery.

To save having to write that H+ = 0.000000040M, he devised the scale of acid in terms of pH, as the negative log of H+ ion activity. (1907)


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Lawrence J HendersonProf Biochemistry and Physiology.

Theory of buffering and of

bicarbonate-hydrogen ion-pCO2

relationship.

The Henderson equation

K = [H+][HCO3-]/[H2CO3]

K is the dissociation constant of carbonic

acid, about 10-3 M

A constant 0.1% of dissolved CO2 in water

is hydrated to carbonic acid.

Therefore it can be simplified to

H2CO3 = dissolved CO2

Where K’ is the apparent dissociation

constant K’ = 10-6.1


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Karl A Hasselbalch 1874-1962Agricultural chemist, Denmark.

Adapted Henderson’s equation to Sørensen’s logarithmic pH by replacing H2CO3 with S.pCO2 creating the

Henderson-Hasselbalch equation:

pH=pK’ + log[HCO3-/(S.pCO2)]

7.40 = 6.10 + log[24/{0.31.40}]Where S (solubility) = 0.031 mM/liter/mmHg at 37oC


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Donald D Van Slyke

1883-1971

Major developer of clinical chemistry in the 1910-50 period. His manometric blood gas apparatus (1924) was used to measure the content in blood of oxygen, carbon dioxide and many other variables.

Laboratories calculated pCO2 using the Henderson-Hasselbalch equation after measuring pH of blood and the total plasma CO2 by the Van Slyke apparatus until the polio epidemics resulted in two new methods: Astrup’s equilibration scheme and Severinghaus modification of the Stow CO2 electrode.


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Poul Astrup 1915-2000

Prof of Clinical Chemistry Univ. of Copenhagen

New method for pCO2

To avoid need for the VanSlyke and Henderson-Hasselbalch method, he devised a method for graphically calculating pCO2 by measuring pH before and again after equilibration of the blood to a known pCO2


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John W Severinghaus

1922

Prof of Anestesia University of California San Francisco

Major developer of blood gas measurents since 1950. His modification (invention) of the CO2 electrode, the first blood gas apparatus (1958), the blood gas ruler, transcutaneous blood gas measurement and pulsoximetry, as well as important work in high altitude respiratory physiology


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Ole Siggaard Andersen 1932

Prof of Clinical Chemistry Univ. of Copenhagen

A student of Astrup, he devised the micro-method and the concept of base excess and ECF base excess, now called SBE, for standard base excess.

His equation for SBE is now used in most blood gas apparatus.

Photo 1999 by JWS


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Content

• Acid-base basic




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First Astrup pH apparatus for

equilibration of blood sample with known Pco2, then repeated pH measurement

1953

Instruments in the acid-base story

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Micro-Astrup pH and reference electrodes, 1957

Radiometer Co, Copenhagen, Denmark

The widely used Astrup equilibration method for estimating blood pCO2 by pH measurement before and after equilibration with gas of known pCO2. The glass pH capillary is “A”, filled by suction from “G”, and then connected to reference electrode “K” in saturated KCl “I”.


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First blood gas apparatus. Severinghaus and Bradley (1958)

O2 electrode consumed so much oxygen it needed stirring and calibration with equilibrated blood.

CO2 electrode

O2 electrodestirrer

tonometer


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ABL-1

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BMS-2 , OSM-3 and ABL-4 ( incl. Ole Siggaard-Andersen at work)

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ABL-700

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Polio victim in Copenhagen epidemic being ventilated manually by medical student through tracheostomy, 1952.

Critical care treatment and the acid-base story

Invasive ventilation

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Non-invasive ventilation in Critical Care around 1955

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To put a patient into a ventilator

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Invasive ventilation in Critical Care in 2003

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Content

• Acid-base basic




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Acid-Base status and Normal Saline versus Lactated Ringer’s solution ?

•The future and Base excess

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NaCl

LactateHC03

KCa

Normal Serum

lactated Ringer

NaCl 0,9%0

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Normal Saline Versus Lactated Ringer's Solution

Normal Serum

lactated Ringer

NaCl 0,9%


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How to interpret the difference in Acid Base Status afterInfusion of Normal Saline and Lactated Ringer’s Solution:

- Dilutional Acidosis versus HyperChloremic Acidosis

- Brønsted’s definition versus Arrhenius definition- Buffer Base (BB) versus Strong Ion Difference (SID)

When adding Lactate and Chloride measument, the interpretation of acid base status may be simple and illustrates that

- Buffer base equals SID as well as - Changes in Buffer Base equals Base Excess


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Electrolyte balance of arterial plasma showing columns of cations and anions of equal height (law of electro-neutrality). The equality of the strong ion difference (SID) and buffer base (BB) is illustrated. The change in concentration of buffer base from normal (at pH = 7.40, pCO2 = 5.3 kPa, and T = 37 C) with opposite sign equals the concentration of titratable hydrogen ion.


(O. Siggaard-Andersen in Encylopedia of Respiratory Medicine 2006)

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Base Excess is a virtual parameter, making some very complex matter simple and clinical useful

Base Excess may continue to exist as the metabolic parameter in Acid-Base status

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Thanks to John W Severinghaus for his kind advice and help

Reykjavik june 2005

Thanks to Ole Siggaard-Andersen for his kind advice and help

Gilleleje 2003

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Advice from your brain and body: ”Use me or loose me”

IHG 05 Base Excess and Critical Care in the past and in the future Ivar Hejde Gøthgen M.D., D.M.Sc.

Documents

acidbase story slide

acid base status

acidbase status slide

bufferlines acid base

acidbase nomogram base

base excess slide

acidbase story instruments

blood mmoll acid base